<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script>
			function doC(){
				var d=document.getElementById("t");
				d.type="checkbox";
			}
		</script>
	</head>
	<body>
		<input type="text"  id="t" name="fff"/>
		<input type="button" value="change t ype" onclick="doC()" />
	</body>
</html>
